A. Technical Field
This invention generally relates to pressure activated engines and compressors. More particularly, this invention is a reciprocating-piston engine having a harmonic oscillator valve controlling the admission of a pressurized expansible fluid into an expansion chamber and an outlet controlled by the motion of the piston allowing the exhaust of working fluid from the expansion chamber. In some embodiments the present invention can also operate as a compressor.
B. Description of the Related Art
Engines that transform the internal energy within a high-pressure expansible fluid into useful mechanical energy, such as steam engines, are well known. Among reciprocating steam engines, the form having the greatest economy and greatest efficiency is the uniflow steam engine. In “Steam-Engine Principles and Practice”, published in 1922, a uniflow engine is disclosed operating with 461 psia superheated steam at a temperature of 1018° F. that produced an indicated efficiency of only 5.67 pounds of steam per indicated horsepower hour, or 37% thermal efficiency. In the uniflow steam engine, the valves controlling the admission of high-pressure supply steam to the cylinder are at an end of the cylinder, while all of the exhaust of expanded, low pressure steam, preferably at sub-atmospheric pressure for highest efficiency, is from vent ports placed around the circumference of the cylinder, and located nearly a full stroke distance away from the inlet valves. Double acting uniflow engines have inlet valves at both ends of the cylinder and vent ports at the middle of the cylinder, while single acting uniflow engines have inlet valves at one end of the cylinder, near the Top Dead Center position, TDC, of the piston with vent ports placed near the Bottom Dead Center position, BDC. The thermodynamic reason for the superior efficiency of the uniflow steam engine design, as opposed to the counter flow design, is that the detrimental phenomenon of hotter steam condensing on relatively colder cylinder walls, thus dropping the pressure on the power stroke, or colder steam vaporizing on relatively hotter cylinder walls, thus increasing the pressure on the recovery stroke, is greatly reduced.
There have been a number of technical challenges in the art of uniflow engines, such as the need to maintain a significant minimum cylinder clearance space, in order to avoid damage produced from overly recompressing steam as the piston approaches TDC. On the other hand, on the exhaust stroke, without recompressing steam all the way to the pressure of the incoming steam, and with a significant minimum cylinder clearance space, the resulting highly non isentropic, rapid inrush of high pressure steam at the time the inlet valve opens and the clearance space fills is detrimental to achieving high thermodynamic efficiency. This rapid inrush also leads to the problem with conventional steam engine inlet valves of “wire drawing”, which occurs when the high velocity flow of steam erodes or scores a pathway in the seating material that remains after the valve is closed, and can cause leakage. A similar “wire drawing” effect also happens as valves are closed, if they do not close quickly and a high velocity flow of steam is allowed to persist overly long. Inlet valves capable of rapid action, in order to enable high expansion ratios at high speed, and to avoid “wire drawing” problems, have been a challenge. Another historical challenge has been the choice of lubricant for the piston and valves, as common engine oils tend to degrade at high temperature.